FIG. 1 shows one example of a conventional drilling system for drilling a well bore in an earth formation. The drilling system includes a drilling rig (10) used to turn a drill string (12), which extends downward into a well bore (14). Connected to the end of the drill string (12) is a drill bit (20).
In drilling applications, electronic devices may be used downhole to acquire information about the drilling operation and/or the earth formation. The electronic devices may need to be operated at temperatures much higher than their rated operational range. As the wells are drilled deeper, the desired operating temperature range for the electronic devices increases.
The electronic devices market is driven primarily by the computer and communications industries. Neither the computer nor communications industries typically have a need to operate electronic devices above 85° C. While there are a few industries, for example, the automobile, aerospace, and oil industries, that have a need to operate electronic devices at such higher temperatures, none of these industries purchase electronic devices in volumes that influence the electronics manufacturers to design electronic devices that operate at such higher temperatures. Accordingly, these industries may operate the electronic devices outside the electronics manufacturer's recommended operating temperature range.
As shown in FIG. 2, an exemplary plastic encapsulated integrated circuit (100) includes an integrated circuit or die (110) encased in a molding compound (102). The die (110) communicates through bond wires (108) between the die (110) and a lead frame (106). The lead frame (106) extends beyond the molding compound (102) so that leads (104) may be attached to a substrate, e.g., printed circuit board, or wire (not shown).
When electronic devices, for example the plastic encapsulated integrated circuit (100 shown in FIG. 2), are operated at high temperature, chemical reactions may cause internal failures to be accelerated and cause premature failure. Furthermore, thermal expansion of dissimilar materials may result in high stresses to develop and cause failure. Typically, the failures are at the wire bonds of the plastic encapsulated integrated circuit (100 shown in FIG. 2). Both the weakening of the wire bond strength due to corrosion reactions combined with high stresses due to coefficient of thermal expansion (CTE) mismatches in the materials within the plastic encapsulated integrated circuit (100) lead to premature failure. Research in the field of high temperature electronics has shown that chemical reactions that cause the weakening of wire bonds are accelerated by the presence of halogens (Br, Cl, Fl, etc.) and Antimony introduced into the molding compound of the electronic devices as flame-retardants.
Mechanisms that cause a plastic encapsulated integrated circuit (100 shown in FIG. 2) to fail at high temperatures have received some attention. Several researchers have found that halogens such as Br, Cl, and Fl introduced into the molding compound as flame-retardants accelerate inter-metallic formation and cause voiding and corrosion leading to wire bond failure. Antimony was also found to accelerate wire bond failures and may affect the wire bonds independently of Br. A chain of reactions that cause these chemicals to weaken the wire bonds was also proposed and partially verified with experiments. A potential solution to the problem of accelerated wire bond failure under high temperatures is the introduction of Pd to gold bond wires to slowdown corrosion. Furthermore, reducing an amount of Br present in a molding compound of a plastic encapsulated integrated circuit (100 shown in FIG. 2) increased longevity of the plastic encapsulated integrated circuit (100 shown in FIG. 2) at high temperatures. A change in construction of a plastic encapsulated integrated circuit (e.g., 100 shown in FIG. 2) is, however, not a practical solution since a manufacturing process of an electronic device is unlikely to be influenced for the reasons discussed above.
Electronic devices, e.g., plastic encapsulated integrated circuits (100 shown in FIG. 2), may be operated safely at temperatures much higher than the rated temperature for a shorter period of time than their intended lifetime. When electronic devices are operated at higher temperatures, however, a failure of the electronic devices may be accelerated. Accordingly, a method and apparatus that are capable of predicting potential failures of electronic devices used in harsh environments are desirable.